Griffith's Transformation Principle

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The transformation principle suggests that bacteria use DNA as their genetic material and are able to exchange their genetic material via a process of transformation. Griffith had theorised the concept of the transformation principle using two strains of bacteria and studied their ability to recombine. Avery and MacLeod followed his studies and suggested DNA was sensitive to DNase, and that the enzyme would destroy the bacteria's ability to exchange genetic material and transform into a new strain. This was then tested in the labs at Wits by second year students where they studied the transformation of ampicillin sensitive E. coli to ampicillin resistant E. coli. The results obtained there were similar to those of Avery and MacLeod,
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The bacteria were heat-killed, and these respective components were extracted and the composition resulted in being similar to that of DNA. They also treated the bacteria with multiple enzymes, such as trypsin, chymotrypsin, ribonuclease and deoxyribonucleodepolymerase, where it was found that only the deoxyribonucleodepolymerase inhibited the formation of smooth Pneumococcus colonies. [Downie. A. W. (1972)] Thus, they confirmed that DNA was the transformation principle in Griffith's experiments. The Avery and MacLeod experiment was replicated in the laboratories at the University of the Witwatersrand. The objective of such was to identify if the results obtained at Wits would run parallel to those of Avery and MacLeod with regard to the nature of the transformation…show more content…
These plates would be those which were treated with RNase, protease, lysozyme and the plate with buffer only. The only plate expected to not have any growth was the plate which was treated with DNase. The DNase would have broken down the double-stranded DNA molecule into its nucleotides and thus, would have been unable to transfer genetic material from the ampicillin resistant strain of E. coli to the ampicillin sensitive strain. Therefore, no new transformants containing ampicillin resistance would have been present and so, the bacteria would have been killed by the ampicillin-containing plate. The experiment conduced at Wits did not correlate with Avery and MacLeod's results entirely. They were able to conclude that DNA is the transforming principle in bacteria, but from the results obtained by the university, the conclusion would have been different.
With regard to the number of transformants per µg DNA, the expected results were to lie between 20 000 and 30 000. The results obtained in the laboratory were shown to be 18 370.37 transformants/ µg. The value calculated does not fall between the expected values, however, it is very close to the results that were expected. Therefore, it can be said that there was little interference in the bacteria's ability to perform
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